[Metakit] Hash view questions

[gary.h.merrill at GSK.COM]

I'm confused about hash views.  I use them, but I'm not sure how some of 
the details of that use is supposed to work.

Looking at Brian's notes on "hash" in the "Metakit for Python" document, I 
see that:

'The mapview must be empty the first time this hash view is used, so that 
Metakit can fill it based on whatever rows are already present in the 
underlying view.'

This seems to imply that you can't "impose" a hash view on an existing 
view.  But I seem to be able to do this.  That is, in an existing storage 
I get an existing view (either via .view() or .getas()) and then create a 
hash view on it.  This does work, doesn't it?

Also, use of the hash view isn't "permanent" -- in the sense that the 
underlying view retains its own integrity (so long as you don't try to 
access it directly while the hash view is "in effect")?  That is, it 
*seems* to work nicely to create a view, define a hash view on it, 
populate the view, drop the hash view, and then commit() so that only the 
underlying view goes into the storage.  This behavior also seems to imply 
that you should be able to lay a hash view on top of an existing view, 
access and update via the hash view, then drop it and commit only the 
underlying view.  Have I missed anything here?

One final question:  Is there a way to create a hash view to hash on a 
particular property?  I seem to frequently want, say, a two-column table 
where I can create one hash view based on the first column and another 
based on the second.

------------------------------
Gary H. Merrill, Principal Scientist
Analysis Applications, Research, and Technologies
GlaxoSmithKline Research and Development
Research Triangle Park, NC
919.483.8456
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